1. Field of the Invention
The present invention relates to a system and method for adaptively controlling the transmit power and data rate at which a communication signal is transmitted between nodes in a wireless ad-hoc communication network. More particularly, the present invention relates to a system and method for selecting an appropriate transmit power and data rate at which a communication signal is transmitted over a link between nodes in a wireless ad-hoc communication network based on factors such as variations in path loss in the link, fading conditions, noise level estimation and overall link quality.
2. Description of the Related Art
In recent years, a type of mobile communications network known as an “ad-hoc” network has been developed. In this type of network, each user terminal (hereinafter “mobile node”) is capable of operating as a base station or router for the other mobile nodes, thus eliminating the need for a fixed infrastructure of base stations. Accordingly, data packets being sent from a source mobile node to a destination mobile node are typically routed through a number of intermediate mobile nodes before reaching the destination mobile node. Details of an ad-hoc network are set forth in U.S. Pat. No. 5,943,322 to Mayor, the entire content of which is incorporated herein by reference.
More sophisticated ad-hoc networks are also being developed which, in addition to enabling mobile nodes to communicate with each other as in a conventional ad-hoc network, further enable the mobile nodes to access a fixed network and thus communicate with other types of user terminals, such as those on the public switched telephone network (PSTN) and on other networks such as the Internet. Details of these types of ad-hoc networks are described in U.S. patent application Ser. No. 09/897,790 entitled “Ad Hoc Peer-to-Peer Mobile Radio Access System Interfaced to the PSTN and Cellular Networks”, filed on Jun. 29, 2001, in U.S. patent application Ser. No. 09/815,157 now U.S. Pat No. 6,807,165 entitled “Time Division Protocol for an Ad-Hoc, Peer-to-Peer Radio Network Having Coordinating Channel Access to Shared Parallel Data Channels with Separate Reservation Channel”, filed on Mar. 22, 2001, and in U.S. patent application Ser. No. 09/815,164 entitled “Prioritized-Routing for an Ad-Hoc, Peer-to-Peer, Mobile Radio Access System”, filed on Mar. 22, 2001, the entire content of each of said patent applications being incorporated herein by reference.
As can be appreciated by one skilled in the art, when a node sends packetized data to a destination node, the node typically checks its routing table to determine whether the destination node is contained in its routing table. If the destination node is contained in the node's routing table, the data is transmitted via a path that leads to the destination node. If the destination node is not listed in the node's routing table, then the packet is sent to one or more other nodes listed in the node's routing table, and those other nodes determine if the destination table is listed in their routing tables. The process continues until the data packet eventually reaches the destination node.
In these types of ad-hoc networks, data transmitted from one station to another is affected by adverse conditions. These conditions may prevent the transmitted data from being correctly received by the destination station. In order to provide a high reliability of data transfer, the transmit power and data rate must be adjusted to proper levels. Although high transmit power and low data rate assure that the signals are received by the receiving station at the highest reliability, they cannot be used without having negative effect on network operation. For example, because high transmit power enables the transmitted signal to be received at distances far away from the transmitter, this prevents the same frequency channel to be used for making other connections between other stations within the range of the high power transmit signal. Furthermore, transmission at a lower data rate typically uses higher energy than at a higher data rate, while requiring a longer period of time for transmitting the same amount of data that could be transmitted quicker at a higher data rate.
Accordingly, a need exists for a system and method for selecting the most appropriate transmit power and data rate at which a communication signal is transmitted over a link between nodes in a wireless ad-hoc communication network.